This invention relates to power cylinders operated by fluid pressure and more particularly to a fluid pressure power cylinder including means to securely lock the piston in a desired position of the piston.
Power cylinders, either pneumatically actuated or hydraulically actuated, find many applications in modern industry. For example, power cylinders are utilized to advance the slide of a tool head in a machine tool so as to bring the cutting tool to a position to operate on a workpiece. If the piston is not locked in its position of adjustment, the associated tool may bounce back and forth or chatter when it is moved against and into the work. As a further example, power cylinders are also conventionally used to operate work holding clamps. It is essential in these situations that the cylinder hold the workpiece securely and that it maintain a holding force on the work, sometimes for long periods of time and sometimes regardless of variations in the size of the work due to permissible work tolerances or other factors. For example, parts such as aircraft wings or the like are sometimes clamped in position and left for days while different machining and assembling operations are performed thereon. It is important in these cases that the power clamps used to hold the part maintain full pressure continuously and that pressure not be relieved or even reduced appreciably at any clamp during the entire period.
It is important therefore, in these and other applications, that the power cylinder include means to ensure that the piston, and thereby the associated tool or clamp, maintains its position of adjustment irrespective of forces exerted against the associated tool or clamp and irrespective of pressure losses in the cylinder.
Various devices have been proposed to allow the piston to be locked in its position of adjustment. One such device, shown in U.S. Pat. No. 3,576,151, includes a ring which is rotated following movement of the piston to its full stroke position to engage pins carried by the piston and thereby lock the piston in its position of adjustment irrespective of any subsequent loss of pressure in the system. Whereas this piston lock arrangement has been generally satisfactory, it does not provide the ability to lock the piston over any significant range of piston positions but rather provides locking only in the full stroke position of the piston.
A further such device, shown in U.S. Pat. No. 5,020,418, allows locking of the piston over a significant range of piston positions but achieves this range of locking in a design that is relatively complex and therefore relatively expensive to produce.